1. Field of the Invention
The present invention relates to a process for forming a film by vapor deposition on a substrate. The invention also pertains to the use of such a film in a lithographic process.
2. Description of the Prior Art
In the field of semiconductor processing, it is generally known to use polysilane materials as positive photoresists. See, for example, U.S. Pat. No. 4,587,205, issued to Harrah, et al. on May 6, 1986, and U.S. Pat. No. 4,588,801, issued to Harrah, et al. on May 13, 1986. See also, West, R., "Polysilane High Polymers and Their Technological Applications," Actual. Chim., (3), 64-70 (1986).
The art discloses a number of methods for the preparation of such polysilane compositions. For example, in U.S. Pat. No. 4,578,495, issued to Soula, et al. on Mar. 25, 1986, polysilanes are prepared by contacting, in an inert atmosphere, at least one disilane with a catalyst system which includes an ionic inorganic salt, M.sup.+ A.sup.-, and a compound that complexes the M.sup.+ cation of the salt. Reference is also made to U.S. Pat. No. 4,667,046, issued to Frey, et al. on May 19, 1987, which provides another method for making polysilanes. In that patent, the method involves reacting at least one methoxy-containing disilane with an SiH-containing silane in the presence of at least one alcoholate, MOR, where M is an alkali metal and R is a select monovalent hydrocarbon radical. Further, in U.S. Pat. No. 4,298,558, issued to Baney, et al. on Nov. 3, 1981, polysilane compositions are prepared by reacting, under anhydrous conditions, a select polysilane with a reagent selected from carbinols, alcoholates and alkyl orthoformates.
Yet another approach for preparing polysilanes is disclosed in U.S. Pat. No. 3,399,223, issued to Atwell, et al. on Aug. 27, 1968. That process involves heating under neutral conditions, at a temperature of 165.degree.-350.degree. C., a select polysilane to effect a redistribution between Si-Si bonds and Si-OR bonds.
In the use of polysilanes as photoresists, the procedure generally involves first preparing the desired polysilane, e.g. by one of the methods described above, and then dissolving it in a suitable solvent. After filtering the solution to remove impurities, the solution is spin applied to a substrate. This approach cannot be followed with many polysilanes, however, because they do not readily dissolve in commonly used solvents. Another drawback is that spin application does not result in a uniform coating of the material over horizontal and vertical surfaces on the substrate.
Efforts have been made to overcome the latter problem, so as to obtain a more uniform coating of photoresist, one technique involving the application of two or more layers. But this method further involves the use of two or more development steps, with a resulting increase in the complexity and cost of the overall process.
Another approach which attempts to obtain a more even coating thickness is disclosed in U.S. Pat. No. 4,675,273, issued to Woods, et al. on Jun. 23, 1987, where a photoresist is formed on a substrate by vapor deposition. However, in practice, the process first requires treating the substrate surface with a suitable activator. Also, the process involves the use of cyanoacrylate monomers; there is no disclosure that any other types of monomers could be satisfactorily employed. Reference is also made to U.S. Pat. No. 4,781,942, issued to Leyden, et al. on Nov. 1, 1988, where a protective layer of a siloxane polymer is deposited on the surface of a substrate. According to this process, a select monomer precursor is reacted with a select oxygen-containing precursor in the presence of radiation, resulting in formation of a siloxane polymer on a substrate.
Thus, there is a need in the art for a process for depositing a film of a polysilane material, which overcomes the disadvantages of spin application, which forms a more uniform coating over horizontal and vertical surfaces on a substrate, and which can be utilized for depositing a variety of polysilanes, not all of which are utilizable by way of spin application.